1. Field of the Invention
This invention relates to a standard measurement scale and markers for defining a standard measurement scale, which are used in photogrammetric analytical measurement systems.
2. Description of the Related Art
For example, photogrammetry measurement is carried out at a traffic accident site. Namely, the traffic accident site is photographed by a camera or cameras, and a survey map is established on the basis of pictures photographed by the camera. Before real distances and lengths can be reproduced on the survey map, a standard measurement scale must be recorded in the pictures.
Conventionally, the standard measurement scale is defined by at least two cone-shaped markers which are formed of, for example, a suitable plastic material. In particular, for example, at a traffic accident site, two markings are indicated on the ground with chalk, and a distance between the markings is obtained using a measuring tape. Then, the cone-shaped markers are positioned at the respective indications. Thereafter, the traffic accident site is photographed by the camera(s), such that the cone-shaped markers are included in the field of view to be photographed.
Before a survey map can be exactly drawn, the cone-shaped markers must be positioned with respect to the indications on the ground, such that an apex of each cone-shaped marker is just above the corresponding indication, because each of the apexes of the cone-shaped markers serves as a reference point for defining a standard measurement scale.
Nevertheless, it is difficult and troublesome to align the apex of the marker with the indication, because the indication is lost from sight due to the enlarged bottom of the cone-shaped marker during positioning. Further, when the ground is not horizontal, i.e., when the ground is sloped, the positioning of the cone-shaped marker is further complicate, because a fine positional adjustment of the cone-shaped marker is necessary before the apex of the cone-shaped marker can exactly coincide with the corresponding indication.
Also, conventionally, the apex of the cone-shaped marker is painted with a light-color, such as white, yellow or the like, so that the apex is conspicuous when recorded in a photographed picture. Nevertheless, the apex of the marker is ot necessarily conspicuously recorded in the picture, e.g., when the tone of color of the background is similar to the apex color.
Furthermore, it is troublesome to obtain a distance between the indications using the measuring tape. Especially, in photogrammetry, in which a reference plane must be defined by at least three reference points, it is necessary to measure the three distances between the three reference points by using the measuring tape.